1. Field of Invention
The present invention relates to a plasma display panel, PDP, and more particularly to a method for manufacturing bus electrodes of a plasma display panel.
2. Description of Related Art
Plasma display panels (PDP) can be divided into two types, the direct current (DC) type and the alternating current (AC) type, according to their electrical driving mode. In FIG. 1, which illustrates a conventional AC-type PDP, glass plates 11, 12 undergo several manufacturing steps in which many functional layers are formed thereon and are then combined together by sealing the periphery of the glass plates 11, 12. A mixed gas with a predetermined ratio is then introduced into the discharge units between the glass plates 11, 12.
In FIG. 1, a plurality of parallel transparent electrodes 111 and bus electrodes 112, a dielectric layer 113 and a protective layer 114 are sequentially formed on the glass plate 11, hereinafter referred to as front plate 11. Similarly, a plurality of parallel address electrodes 121, a plurality of parallel barrier ribs 122, a fluorescencer 123 and a dielectric layer 124 are formed on the glass plate 12, hereinafter referred to as back plate 12. It is noticed that the barrier ribs 122 can be formed as grid structure. One transparent electrode 111 on the front plate 11 and one address electrode 121 on the back plate 12, transparent electrode 111 and address electrode 121 being perpendicularly crossed, compose a discharge unit. When a voltage is applied to a specific discharge unit, gas discharge occurs at the discharge unit between the dielectric layers 113 and 124 to induce emission of a colored visible light from the fluorescencer 123.
FIG. 2 is a schematic, cross-sectional view corresponding to FIG. 1. In a conventional AC-type PDP 10, referring to FIGS. 1 and 2 simultaneously, a plurality of parallel-arranged transparent electrodes 111 are formed on the front plate 11. Each of the transparent electrodes 111 correspondingly has a bus electrode 112 to reduce linear resistance of the transparent electrodes 111. In one discharge unit 13, a three-electrode structure, including an X electrode and an Y electrode of the transparent electrode 111 on the front plate 11 and an address electrode 121 on the back plate 12, is generally employed. When a voltage is applied to the above three electrodes of a specific discharge unit 13 to induce discharge, the mixed gas in the discharge unit 13 emits ultraviolet (UV) rays to light the fluorescencer 123 inside the discharge unit 13. The fluorescencer 123 then emits a visible light, such as a red (R), green (G) or blue (B) light. An image is thus produced by scanning the discharge unit array.
FIG. 3 is a schematic, top view of the front plate 11 of the conventional AC-type PDP 10. A pair of transparent electrodes 111 arranged in parallel is shown in this figure. A plurality of transparent electrodes 111 arranged in parallel are built in the front plate 11. The transparent electrodes 111 have a higher resistance; therefore, a plurality of bus electrodes 112 is formed over the corresponding transparent electrodes 111 to help discharge and reduce the resistance of the transparent electrodes 111. The part of the bus electrodes 112 indicated by the number 300 and 302 extend out the transparent electrodes 111 to connect with the control circuit (not shown in the figure) to control the discharge of the transparent electrodes 111.
Two coating processes are used to form the bus electrodes 112 as shown in the FIG. 4. First, a Ru-containing layer 40 is coated on the front plate 11 and the transparent electrodes 111. Then, an Ag-containing layer 42 is coated over the Ru-containing layer 40. The Ru-containing layer 40 is used to help the Ag-containing layer 42 to adhere over the transparent electrodes 111. Referring to FIG. 5A, a photolithography process is performed to define the bus electrodes 112. Next, a dielectric layer 113 is formed on the front plate 11 to cover the transparent electrodes 111 and bus electrodes 112. A protective layer 114 is formed on the dielectric layer 113.
However, the difference in material characteristics between the Ru-containing layer 40 and the Ag-containing layer 42 causes a beveled edge in the defined bus electrodes 112. The defined bus electrodes 112 are shown in the FIG. 5B, which is an enlargement of FIG. 5A. The width (x direction) and the length (z direction) of the Ru-containing layer 40 are both less than the width and length of the Ag-containing layer 42. In other words, the area in the x-z plane of the Ru-containing layer 40 is less than the area in the x-z plane of the Ag-containing layer 42. It is very possible for the Ag-containing layer 42 to peel away from the Ru-containing layer 40 in the z direction at the two ends of the bus electrodes 112.
A thermal process is often performed during manufacturing the dielectric layer 113. Because of the stress resulting from the thermal process, peeling may occur at the beveled edge in the bus electrodes 112. However, the peeling is suppressed in this part of the bus electrodes covered by the dielectric layer 113. Therefore, the extension 300 and 302 of the bus electrodes as shown in FIG. 3 often break because of peeling.
FIG. 6 shows a cross-sectional view of FIG. 5 from the AA′ line. The difference in material characteristics between the Ru-containing layer 40 and the Ag-containing layer 42 sometimes cause a beveled edge in the bus electrodes 112. The part 600 extending out of the dielectric layer 113 often causes peeling because of thermal stress. Serious peeling causes the bus electrodes 112 to break. Extended part 600 is used to connect with the control circuit (not shown in the figure); however, the panel cannot be connected to the control circuit once the extended part 600 breaks.